Field of the Invention
The present invention relates to an image reading apparatus, such as a scanner, which is configured to read an image (hereinafter referred to as “document image”) of a document.
Description of the Related Art
An image reading apparatus is connected to an image forming apparatus, such as a copier or a multifunction apparatus, and is used to read a document image in copying or facsimile transmission. Moreover, the image reading apparatus may be connected to an information processing apparatus, such as a personal computer, and be used as a scanner. When reading a plurality of documents successively one by one, the image reading apparatus includes a document conveying device, such as an automatic document feeder (ADF). The image reading apparatus is configured to take in the documents successively with the document conveying device so that document images may be read efficiently.
The image reading apparatus including the document conveying device is configured to read the document images with a scanner while conveying the documents, which have been taken in one by one from the document conveying device. The scanner includes a light emitting part configured to irradiate a document with light, and a light receiving part configured to receive reflected light, which has been reflected by the document. The image reading apparatus is configured to read a document image based on the reflected light received by the light receiving part. The image reading apparatus may have the structure including two scanners so as to sandwich a conveying path of the document. When including the two scanners, the image reading apparatus may read images on two sides (front side and back side) of the document by conveying the document once.
The light emitting part of the scanner normally has the structure in which a plurality of light emitting elements are arranged linearly. The light receiving part has the structure in which a plurality of light receiving elements are arranged linearly. The scanner may read the document image line by line in order with a direction orthogonal to the conveying direction of the document being a main scanning direction. In such configuration, accuracy in installing the scanner in the image reading apparatus affects quality of the read document image. For example, an irradiated region irradiated by the light emitting elements and a reading line of the light receiving elements may be inclined with respect to the main scanning direction. In this specification, such an incident is referred to as an inclination of the scanner, and an inclination angle is referred to as an inclination amount. In this case, the scanner is configured to scan the document in accordance with the inclination of the reading line, and hence to read an inclined document image. As a result, geometric quality of the read document image may be reduced.
In Japanese Patent Application Laid-open No. 2004-56524, there is disclosed an image reading apparatus, in which a pattern arranged near a reference scale for document alignment is read by a scanner (optical device element), and in which a document image is shifted based on a result of the reading to correct skew. In Japanese Patent Application Laid-open No. 2010-93760, there is disclosed an image reading apparatus, in which an inclination of a scanner is detected based on a result of reading a reference pattern formed inside a housing. This image reading apparatus is configured to correct a document image, which has been read by the scanner, depending on the inclination of the scanner. As described above, in the image reading apparatus in each of Japanese Patent Application Laid-open Nos. 2004-56524 and 2010-93760, an inclination amount of the scanner is detected based on the reference pattern, and an inclination of the document image is corrected depending on a result of the detection. In Japanese Patent Application Laid-open No. 2010-118911, there is disclosed an image reading apparatus, in which a skew amount of a conveyed document is detected, and in which a read document image is corrected depending on the detected skew amount of the document.
With the image reading apparatus in each of Japanese Patent Application Laid-open Nos. 2004-56524 and 2010-93760, the inclination amount of the scanner is detected based on the reference pattern, but when the reference pattern itself is inclined, an accurate inclination amount of the scanner cannot be detected. In addition, there is a need to drive the scanner in order to read the reference pattern, and accuracy of a reading operation of the scanner also affects accurate detection of the inclination amount of the scanner. With the image reading apparatus in Japanese Patent Application Laid-open No. 2010-118911, the skew amount of the conveyed document may be detected, but the inclination amount of the scanner is not taken into consideration. To address the above-mentioned problems, there is a demand for a technology of reliably detecting the inclination amount of the scanner. The present invention provides an image reading apparatus, which is configured to detect an inclination amount of a scanner more accurately than in the related art, and to read a high-quality document image.